Permeability of Ablative Materials Under Rarefied Gas Conditions

White, Craig; Scanlon, Thomas; Brown, Richard E.

doi:10.2514/1.a33279

Cited by 25 publications

(15 citation statements)

References 31 publications

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“…As direct simulation Monte Carlo (DSMC) method is extremely expensive for simulating lowspeed flows in tight porous media [13], the kinetic model equations such as Bhatnagar-Gross-Krook (BGK) [14], ellipsoidal-statistical BGK (ES-BGK) [15] or Shakhov (S) [16] model, can be solved to provide accurate results to unravel gas transport mechanisms at the pore scale. Among various numerical methods for solving the Boltzmann model equations, lattice Boltzmann model (LBM) [17] is well developed and extensively used for modelling flows in porous media thanks to the ease of boundary implementation on complex surfaces [18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Pore-scale simulations of rarefied gas flows in ultra-tight porous media

Zhu

et al. 2019

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An in-depth understanding of gas transport in ultra-tight porous media is the key to quantifying flow properties of shale rocks with pore space as small as a few nanometers, where the gas rarefaction effects play a major role. As the conventional fluid mechanics theory fails to describe non-equilibrium rarefied flow, we resort to the gas kinetic theory and directly simulate gas flow inside the porous media utilising the digital images of porous media where the pore space is resolved. The Boltzmann model equation is solved by the discrete velocity method (DVM), which can accurately predict the permeability enhancement caused by rarefaction effects. Our simulations for different porous media show that the commonly-used standard lattice Boltzmann method (LBM) cannot describe rarefaction effects, although the kinetic boundary condition, which helps to capture velocity-slip, can extend the validity of the LBM to the slip flow regime. The heuristic Klinkenberg-type models proposed for all the flow regimes often involve many unknown empirical parameters, which may be calibrated by our simulations. However, these parameters are different for each porous medium and also depend on flow conditions, so these models are not of any prac-1 tical use. By contrast, our kinetic solver can accurately predict apparent permeability without introducing any empirical parameters, which lays firm foundation for upscaling. As the large flow paths with least flow resistance dominate the overall permeability, the requirement on the velocityspace resolution is significantly reduced for our DVM simulations to predict accurate permeability with affordable computational costs, which offers a promising new way for digital rock analysis.

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Section: Introductionmentioning

confidence: 99%

Pore-scale simulations of rarefied gas flows in ultra-tight porous media

Zhu

et al. 2019

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“…White et al [2] used the DSMC to investigate the permeabilities of two ablative materials, one cork-phenolic and one carbon-phenolic, in both their virgin and pyrolyzed states. They performed micro-CT scans of samples and imported the 35 corresponding meshes for use in DSMC.…”

Section: Introductionmentioning

confidence: 99%

High temperature permeability of fibrous materials using direct simulation Monte Carlo

Borner

Panerai

Mansour

2017

International Journal of Heat and Mass Transfer

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Porous carbon fiber materials are used as effective insulators in many applications where high temperatures are involved. In particular, they are used as the substrate of ablative thermal protection materials for atmospheric entry systems. In this application and in many other industrial uses, quantifying the permeability of porous materials is needed to compute the flow rate of gases through them, under certain environmental conditions. In this work, direct simulation Monte Carlo (DSMC) simulations are used to compute permeability of several fibrous substrates to high temperature gases. The actual porous geometry of the materials is digitized using X-ray microtomography. Numerical results at various pressures and Knudsen numbers are compared with experimental data published in the literature. The method confirms that the pressure dependence of effective gas permeability is well represented by the Klinkenberg formulation.The method is validated by showing close agreement between measurements of permeability from simulations and experimental investigations. Four carbon fiber materials with different microstructures are investigated. We show that the permeability strongly depends on the pore size distribution, as well as on 20 ing the Boltzmann equation. It was originally proposed for rarefied and transitional flows but has since been applied to near-continuum and continuum flows.DSMC can provide an accurate model for the entire boundary layer including the flow within the microstructure, where the size of the fibers may approach the mean-free-path of the flow. As the permeability of a porous material is a 25 function of the distribution of its micropores, in this paper, the computational domain for DSMC simulations is obtained from three-dimensional (3D) images

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“…Generation from micro-CT scans Numerical meshes can be generated from µCT scans of real porous media, as described in [8]. A three-dimensional representation of the pore arrangement within the material can be extracted and further processed to obtain a castellated mesh similar to the one shown in Figure 2(a).…”

Section: Porous Media Mesh Generationmentioning

confidence: 99%

Effective diffusivity in porous media under rarefied gas conditions

Casseau¹,

White²

2019

31st International Symposium on Rarefied Gas Dynamics: Rgd31

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For future space missions in which soft landings on extra-terrestrial bodies will be required, it is important to understand the interaction of the propulsion system with the surface of the body. During the landing phase, the porous surface regolith can become contaminated with the exhaust products of the rocket plume, and this contamination must be minimised if sample return from the landing site is the goal of the mission. How far in-depth the exhaust products can reach depends on the effective diffusivity of the gas in the porous surface regolith material. The purpose of this work is to study the influence of temperature, gas number density, and adsorption parameters on the effective diffusivity in highly porous media under rarefied conditions. The procedure to recover the effective diffusivity, using direct simulation Monte Carlo, from a real sample is presented, along with trends as parameters are being varied, which will prove informative for later use of simplified engineering methodologies that assume a homogeneous porous structure.

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Permeability of Ablative Materials Under Rarefied Gas Conditions

Cited by 25 publications

References 31 publications

Pore-scale simulations of rarefied gas flows in ultra-tight porous media

Pore-scale simulations of rarefied gas flows in ultra-tight porous media

High temperature permeability of fibrous materials using direct simulation Monte Carlo

Effective diffusivity in porous media under rarefied gas conditions

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